Mercedes-Benz Hybrid Vehicle – No Start Problem

Mercedes-Benz hybrid vehicles such as the S400 are notorious for having hybrid issues that lead to no-start engine conditions. The most common Mercedes-Benz hybrid problems that won’t allow you to start the engine are caused by either a faulty power electronic module (part number 0009064703) or a defective hybrid battery.

At the time of this article, we diagnosed a lot of Mercedes-Benz S400 vehicles with no start problems. We found that 50% of them wouldn’t start due to the failure of the Power Electronic module. The other 50% would not start due to the failure of the high-voltage hybrid battery.

To find out why an S400 won’t start, running a full system scan and getting a report of all the STORED and CURRENT fault codes is important.

Symptoms

Symptoms of a faulty power electronic module on a Mercedes-Benz S400 Hybrid:

• The vehicle won’t start.
• Vehicle starts intermittently
• Dash lights, ignition turn on, the car won’t start.

You will need a good scanner, such as the YOUCANIC Full System Scanner, to diagnose Mercedes-Benz problems.

Whatever scanner you use must show factory codes, NOT generic P codes. Codes like N129/1 (a  letter, a number, and a dash). It must also read the lithium battery’s separate cell voltage and talk to the “inverter” and “power supply unit.”

Power Electronics Module

Based on the experience of the YOUCANIC team, the most common problem with the Mercedes-Benz S400 Hybrid is the power electronic module (sometimes called a power inverter).

The function of this module is to receive commands from hybrid ECM via CAN-BUS Network and control inverter energy flow to and from the battery and engine. It can control the speed and timing of an electric motor in unison with an Internal combustion engine. It also controls and monitors other components like batteries, charging, and related modules.

The power electronic module should not be confused with the DC/DC converter.  The power electronic module is mounted on the side of the engine/transmission, below the right exhaust manifold, and on the passenger side.

The three-phase electrical connector melts, which means you can no longer start the engine since the electrical motor is used for starting. Remember that the S400 hybrid has no starter; instead, it uses the electric motor mounted in front of the torque converter.

Replacing the Power Electronic Moule at a Mercedes-Benz dealership costs between $10,500 and $12,000. This repair can be done at a fraction of that cost by our team or an independent repair shop. For more help, see How to replace the Mercedes-Benz Power Electronic module.

The good news is that a used or refurbished power electronic unit does not need to be programmed. After the repair, fault codes must be cleared with a Mercedes-Benz scanner.

The fault codes will be stored in Power Electronic Module (SG-EM) and Engine Control Unit (ECU):

• U011000 – Communication with control unit Electric machine A has a malfunction.
• U011081 – Communication with control unit Electric machine A has a malfunction. Incorrect data were received.

A faulty power electronic module triggers these codes. You can buy a refurbished power electronic module (0009064703) online.

The following part numbers are often associated with the power electronic module.

• 0009064703 / 0009065802 / A0009065802
• A 000 906 58 02, 0005844147 / A0005844147
• A 000 584 41 47, 2213430400 / A2213430400,
• 2213430300 / A2213430300, A2213431100,
• 2213430900 / A2213430900, 2213430500,
• 2213400400 / A2213400400, 2213400300
• A2213400300, 2213400600 / A2213400600
• 2213400500 / A221340050

Mercedes-Benz has issued a few different numbers for the power electronic module as the unit has gone over multiple revisions.

Other reasons why your S400 Hybrid may not start include:

• Hybrid battery failure is a very common failure.
• Faulty inverter – The inverter is located behind the right side fender.  It is not a common issue.
• Faulty A/C compressor – Common

To find out why your S400 Hybrid won’t start, you must read the Battery Management System module’s fault codes. It is also essential to run a full system scan to determine fault codes in other modules. An S400 may also not start for other reasons, sometimes unrelated to the hybrid system. For example, other reasons why a Mercedes-Benz S-Class won’t start include:

• Ignition Switch –  EIS,
• Intelligent Servo Module – ISM,
• Engine Control Unit – ECU
• Weak or dead 12-volt battery.
• Stored fault codes that need to be cleared.

Let’s look at some of the most common issues we mentioned above.

Hybrid Battery

Another common problem with the Mercedes-Benz S400 Hybrid is the failure of the hybrid battery, explained in detail here.

Two (2) types of electrical systems are being implemented in a hybrid system. One is the 12-volt electrical system powered by a 12-volt onboard battery. The 12-volt system powers almost 90 percent of the car, including lights, entertainment, horn, etc.

The high-voltage electrical system is powered by a battery with>100 volts DC. A hybrid Battery, high Voltage, or HV battery, is the Hybrid electric motor’s powerhouse.

Its primary purpose is to power the Hybrid electric motor to help the Internal combustion engine with its load. It also acts as a starter for the Internal Combustion Engine. The HV battery should have a 15% charge for an Internal Combustion Engine to start. You can check the charge level via the command by going to System > Hybrid Charge.

Common fault codes that show up as stored or current in the battery management module (SG-BMS):

• 180F00 – The high voltage battery malfunctioned during the recovery phase.
• 0BBD00 – The limit value for the difference between the high-voltage battery module cell voltages has been exceeded.
• 0BBE00 – The cell voltages in the high-voltage battery module are different.
• 0A7D00 – The charge level of the high-voltage battery module is low.
• 180C00, 180500 – The hardware monitoring function has detected a fault in the control unit.
• 0A1F04 – There is an internal fault in the control unit Battery. There is an internal fault.
• 0AE886 – The temperature sensor D of the high voltage battery has an electrical fault. There is an incorrect signal.
• 0ACA86 – The temperature sensor C of the high voltage battery has an electrical fault. There is an incorrect signal.
• 0AC586 – The temperature sensor B of the high voltage battery has an electrical fault. There is an incorrect signal.
• 0A9B86 – The temperature sensor A of the high voltage battery has an electrical fault. There is an incorrect signal.
• 0A1F96 – There is an internal fault in the control unit Battery. There is an internal component fault.
• 0A1F00 – There is an internal fault in the control unit Battery.

DC/DC Converter

Sometimes, the DC-to-DC converter goes bad, but this failure is infrequent. When it fails, it can not transfer 130 to 12 Volts and vice versa. Follow this guide to learn more about the Mercedes-Benz DC/DC converter and how to replace it. 

A/C Compressor

Another problem with the S400 is a defective A/C compressor, preventing the engine from starting.

The AC compressor is the heart of the air conditioning system. In Internal Combustion engine cars, the engine can operate normally with a faulty AC compressor. In a Hybrid System, however, the refrigerant from the AC compressor’s refrigerant serves as a cooling mechanism for the battery.

A Hybrid AC Compressor is also operated by a high-voltage DC rather than a belt to a pulley on an Internal Combustion engine. The ECM protects the battery from overheating by monitoring the AC status and taking actions such as taking the CAN-BUS communication off when the problem is detected.

The AC compressor runs on high voltage, which is not belt-driven. There is a 60A inline fuse mounted on top of the transmission.

The yellow cable runs from the hybrid battery to Power Electronic Module and AC compressor. The 60A fuse protects the AC compressor, not the Power Electronic module.

Service Campaign

It is important to note that Mercedes-Benz had issued a service campaign 2012080004, for this problem. We called to check with the dealer on several S400 Hybrids, and according to the service manager, the dealer performed the service for both cases.

The dealer verifies the part number. If the vehicle is equipped with the Power Electronics module’s early model, the dealer replaces it free of charge. Our S400 had the “newer” version of the power electronic module, so the dealer did not replace the power electronic module. Yet, even the “newer” version of the power electronic module is still failing.

Because the Power Electronic module is mounted next to the exhaust manifold, the chances of the new unit failing eventually remain high.

How to diagnose a Mercedes-Benz Hybrid that doesn’t start?

1. Plug the YOUCANIC scanner into the OBD2 port.
2. Select the Mercedes-Benz model.
3. Go to Control Units
4. Read the fault codes from these modules.
   – ME Motor Electrnoic ECU
   – SG BMS (Battery Management System)
   – Power Electronics Module
   – DC/DC Control Unit
5. Send the fault codes to support@youcanic, and we can give you an idea of what is wrong.

Based on our experience, if the vehicle has between 50,000 and 80,000 miles, the most likely problem is the failure of the hybrid battery. If the vehicle has between 90,000 and 125,000 miles, then it is likely that the power electronic module has failed.

Could you work on your Mercedes-Benz S-400 Hybrid on your own?

As explained in the sections above, there is a high risk of injury or death due to electric shock from the High Voltage System. Based on this, we only recommend that trained mechanics work on the high-voltage hybrid system.

Non-contact electric shock can also happen due to High voltage arc. Also, you must buy expensive safety gear before working on the S-400 Hybrid.
Below are a sample of procedures for just disconnecting the High Voltage System:

1. Locate the onboard 12-volt battery.
2. Disconnect 12v onboard battery ground line.
3. Use a voltage tester to ensure no voltage is passing from the charging point of the pre-fuse box and the ground.
4. This would ensure no transient voltage is stuck between the onboard and auxiliary batteries.
5. It would also ensure that the auxiliary battery does not continue to supply the vehicle.
6. Wear your protective equipment, including electric-resistant globes, an anti-arc jacket, and a helmet with a face shield.
7. You can now disconnect the high-voltage connection from the high-voltage battery module.
8. Safely stick tape on the high-voltage connector and, as much as possible, label it with a warning.

Could a lousy starter be why the Mercedes-Benz S400 won’t start?

No. The Mercedes-Benz S400 W221 hybrid does not have an engine starter.

There is a lot of misinformation online regarding the Mercedes-Benz hybrid vehicles.

For example, RepairPal says that a bad starter is one of the most common reasons a Mercedes-Benz won’t start and gives it a 20% chance. This is inaccurate because this vehicle does not have a starter at all.

The engine of an S400 hybrid is started by the electric motor, which serves the starter function.

Should I buy a Mercedes-Benz Hybrid?

Mercedes-Benz hybrid vehicles are challenging to repair. Most auto mechanics will not repair these vehicles. We have even seen cases where a Mercedes-Benz dealership had difficulty diagnosing an S400 Hybrid vehicle.

If you own a Mercedes-Benz S400 that won’t start, find an expert who knows these vehicles. Finding auto mechanics trained to work on the Mercedes-Benz Hybrid system is difficult. Even Mercedes-Benz dealerships have a limited number of mechanics that can work on hybrid models.

Working on the hybrid system can be dangerous since dealing with a high voltage (130 Volt) can cause injuries and death if you do not take the required precautions.

Sample Procedures for Disconnecting a Hybrid Battery

Locate the onboard 12-volt battery.

1.  Disconnect 12v onboard battery ground line.
2. Use a voltage tester to ensure no voltage is passing from the charging point of the pre-fuse box and the ground.
3. This would ensure no transient voltage is stuck between the onboard and auxiliary batteries.
4. It would also ensure that the auxiliary battery does not continue to supply the vehicle.
5. Wear your protective equipment, including electric-resistant globes, an anti-arc jacket, and a helmet with a face shield.
6. You can now disconnect the High Voltage connection from the high-voltage battery module.
7. Safely stick tape on the high-voltage connector and, as much as possible, label it with a warning.

You may refer to this link for the complete instructions.

Get Help

If you are having issues with the Hybrid, please “contact the YOUCANIC” team with any questions that you may have.

We can help you troubleshoot the problem FREE of charge if you send us the codes.  We need the codes from these four modules:

• Engine ECU,
• DC/DC converter,
• BMS,
• Power Electronics Module.

Once we have the codes, we can tell you if you have a bad power electronic module, hybrid battery, or both.

If your vehicle is at the dealership or mechanic, ask them for the list of codes and send them to us.    If you want to ship the car to Baltimore, we can repair it at a fraction of the dealer’s cost.  We love these cars and believe it is a sin to pay over $10k to keep them running.

Definition of Terms

• CAN-BUS – Control Area Network. It serves as a channel of communication between various control modules.
• DC- Direct Current (Energy from the battery measured in volts).
• ECM   – Electronic Control Module (Main Control Module)
• EMCM – Power Electronic Module, Motor Controller Module, or Electric Motor ECU.
• HV – High Voltage

We hope you find the Mercedes-Benz Hybrid Vehicle – No Start Problem guide helpful. Check these troubleshooting and repair guides for more help on your Mercedes-Benz.